The proposed research contains two major sections. In the first section we aim at elucidating the dynamic properties of E. coli tRNA fmet-Met-RS (methionyl-tRNA synthetase) recognition. In the second section, we aim at elucidating the structural organization of rat liver aminoacyl-tRNA synthetase complexes and the functional significance of complex formation. Nanosecond fluorescence life time measurements of tRNA-synthetase complexes will be used to resolve the relative concentrations of the complexes before and after the conformation transition of Met-RS. Competition with tRNA fragments will be analyzed to identify the location of the dynamic binding sites. Nanosecond fluorescence anisotropy decay of the cognate and non-cognate tRNAs associated with the synthetase will be determined to correlate the segmental flexibility of enzyme-bound tRNA chains with the specificity of enzymatic aminoacylation. The structural organization of rat liver aminoacyl tRNA synthetase complex will be analyzed further to obtain the molecular parameters and the spatial arrangement of the synthetase complexes. The possible protein biosynthesis control and compartmentation of protein synthesis machinery as the result of complex formation of the synthetases will be examined in cell-free in vitro translation system. Investigation in these two systems should provide insight to the structure and function of the interaction of macromolecules.